1. This invention relates to vehicle hydraulic brake systems and, more particularly, to a hydraulic brake system utilizing a proportioning valve which responds to the load of the vehicle to vary the braking effort produced by the rear wheel brake components.
2. Prior use of a rear brake proportioning valve in a hydraulic braking system include the 1984-1985 Chrysler Corporation built T-115 Van and Wagon, sold under the names: Plymouth "Voyager" and Dodge "Minivan" or "Caravan." In these vehicles, a proportioning valve in the hydraulic brake system is mounted to a body member slightly forward of the rear axle and slightly to the left of the vehicle center line. A connector assembly is attached to the rear axle rightwardly of the proportioning valve. The connector includes an elongated tension type spring extending between the axle and the input of the proportioning valve. When the vehicle is lightly loaded, the relative positions of the axle and the proportioning valve produces a relatively slight extension of the spring. As the vehicle load increases, particularly near the rearward portion of the vehicle, the extension of the tension spring is increased as the vehicle body moves downward with respect to the axle. Resultantly, the spring exerts an increased force input on the proportioning valve which results in the valve directing an increased brake fluid pressure to the brake components of the rear wheels for greater rear braking effort.
The aforedescribed brake system operates quite satisfactorily. However, the mid-axle location of the valve and connector assembly is not always convenient on other vehicles due to space considerations and interference with the body and other components. Also, a spare tire stored immediately to the rear of the brake proportioning components and the above described arrangement results in crowding. It would be desirable to locate the brake proportioning components elsewhere to permit better accessibility of the spare tire and greater flexibility in available spare tire dimensions.
The subject invention which is described in more detail hereinafter concerns an improved hydraulic brake system with a relocated proportioning valve responsive to vehicle loading. The proportioning valve and related components are relocated to a more desirable position in front of the rear suspension spring. Therefore, other means are provided to sense and transmit vehicle loading.
The above identified Chrysler Corporation brake system is generally related to the subject invention. Other related patents are discussed hereinafter. U.S. Pat. Nos. 4,150,855 and 4,325,581 relate to a load responsive brake proportioning valve for brake systems, but are specifically designed for use with coil type suspension springs of a vehicle. In both of the devices, the brake proportioning device is configured and arranged to be mounted mostly within the central portion of the coil spring of the vehicle suspension. Both devices receive force inputs directly from the suspension spring through levers 64 and 66 in the '855 patent and through resilient or elastomeric members in the '581 patent.
U.S. Pat. No. 3,975,062 discloses a device responsive to vehicle deceleration for modifying brake action. The deceleration valving device is connected by linkage to an anti-roll bar to respond to suspension related conditions of the vehicle.
U.S. Pat. Nos. 2,498,438; 3,460,871; 3,884,532; and 4,012,079 disclose brake proportioning systems using a proportioning valve responsive to movement of a suspension spring, particularly of the leaf type construction commonly used in association with the rear axle of a vehicle. In addition, the British Pat. No. 957878 assigned to Daimler-Benz discloses a brake proportioning system utilizing a lever pivoted at its midpoint with a first arm connected to an end portion of the leaf spring and with a second arm operating a fluid valve.
There are other brake proportioning devices which are generally relevant to the subject application. The following U.S. patents are in this category: Nos. 2,523,057; 3,149,886; 3,199,928; 3,512,845; 3,684,329; 2,927,916; 3,936,097; 4,060,283; 0,090,740; and 4,445,725. A common feature of these patents is a brake modifying device directly responsive to axle position. It is not believed that these patents are more relevant to the subject invention of this application than the above-described Chrysler system utilized on the T-115 vehicle.